1. Field of the Invention
The present invention relates generally to the delivery of pharmaceutical agents from the blood stream to the human brain and other organs or tissues that express the human insulin receptor. More particularly, the present invention involves the development of “humanized” monoclonal antibodies (MAb) that may be attached to pharmaceutical agents to form compounds that are able to readily bind to the human insulin receptor (HIR). The compounds are able to cross the human blood brain barrier (BBB) by way of insulin receptors located on the brain capillary endothelium. Once across the BBB, the humanized monoclonal antibody/pharmaceutical agent compounds are also capable of undergoing receptor mediated endocytosis into brain cells via insulin receptors located on the brain cells.
2. Description of Related Art
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference. For convenience, the reference materials are identified by author and date and grouped in the appended bibliography.
The BBB is a system-wide membrane barrier that prevents the brain uptake of circulating drugs, protein therapeutics, antisense drugs, and gene medicines. Drugs or genes can be delivered to the human brain for the treatment of serious brain disease either (a) by injecting the drug or gene directly into the brain, thus bypassing the BBB, or (b) by injecting the drug or gene into the bloodstream so that the drug or gene enters the brain via the transvascular route across the BBB. With intra-cerebral administration of the drug, it is necessary to drill a hole in the head and perform a procedure called craniotomy. In addition to being expensive and highly invasive, this craniotomy based drug delivery to the brain approach is ineffective, because the drug or gene is only delivered to a tiny volume of the brain at the tip of the injection needle. The only way the drug or gene can be distributed widely in the brain is the transvascular route following injection into the bloodstream. However, this latter approach requires the ability to undergo transport across the BBB. The BBB has proven to be a very difficult and stubborn barrier to traverse safely.
Prior work has shown that drugs or gene medicines can be ferried across the BBB using molecular Trojan horses that bind to BBB receptor/transport systems. These Trojan horses may be modified proteins, endogenous peptides, or peptidomimetic monoclonal antibodies (MAb's). For example, HIR MAb 83-14 is a murine MAb that binds to the human insulin receptor (HIR). This binding triggers transport across the BBB of MAb 83-14 (Pardridge et al, 1995), and any drug or gene payload attached to the MAb (Wu et al., 1997).
The use of molecular Trojan horses to ferry drugs or genes across the BBB is described in U.S. Pat. Nos. 4,801,575 and 6,372,250. The linking of drugs to MAb transport vectors is facilitated with use of avidin-biotin technology. In this approach, the drug or protein therapeutic is monobiotinylated and bound to a conjugate of the antibody vector and avidin or streptavidin. The use of avidin-biotin technology to facilitate linking of drugs to antibody-based transport vectors is described in U.S. Pat. No. 6,287,792. Fusion proteins have also been used where a drug is genetically fused to the MAb transport vector.
HIRMAb 83-14 has been shown to rapidly undergo transport across the BBB of a living Rhesus monkey, and to bind avidly to isolated human brain capillaries, which are the anatomical substrate of the human BBB (see Pardridge et al., 1995). In either case, the activity of the HIRMAb 83-14 with respect to binding and transport at the primate or human BBB is more than 10-fold greater than the binding or transport of other peptidomimetic MAb's that may target other BBB receptors such as the transferrin receptor (Pardridge, 1997). To date, HIRMAb 83-14 is the most active BBB transport vector known (Pardridge, 1997). On this basis, the HIRMAb 83-14 has proven to be a very useful agent for the delivery of drugs to the primate brain in vivo, and would also be highly active for brain drug or gene delivery to the brain in humans.
HIRMAb 83-14 cannot be used in humans because this mouse protein will be immunogenic. Genetically engineered forms of HIRMAb 83-14 might be used in humans in either the form of a chimeric antibody or a genetically engineered “humanized” HIRMAb. However, in order to perform the genetic engineering and production of either a chimeric or a humanized antibody, it is necessary to first clone the variable region of the antibody heavy chain (VH) and the variable region of the antibody light chain (VL). Following cloning of the VH and VL genes, the genes must be sequenced and the amino acid sequence deduced from the nucleotide sequence. With this amino acid sequence, using technologies known to those skilled in the art (Foote et al., 1992), it may be possible to perform humanization of the murine HIRMAb 83-14. However, HIRMAb 83-14 may lose biological activity following the humanization (Pichla et al., 1997). Therefore, it is uncertain as to whether the murine HIRMAb can be humanized with retention of biological activity.
A chimeric form of the HIRMAb 83-14 has been genetically engineered, and the chimeric antibody binds to the HIR and is transported into the primate brain (Coloma et al., 2000). However, a chimeric antibody retains the entire mouse FR for both the VH and the VL, and because of this, chimeric antibodies are still immunogenic in humans (Bruggemann et al., 1989). In contrast to the chimeric antibody, a humanized antibody would use the human FR amino acid sequences for both the VH and the VL and retain only the murine amino acids for the 3 complementarity determining regions (CDRs) of the VH and 3 CDRs of the VL. Not all murine MAb's can be humanized, because there is a loss of biological activity when the murine FR's are replaced by human FR sequences (Pichla et al., 1997). The biological activity of the antibody can be restored by substituting back certain mouse FR amino acids (see U.S. Pat. No. 5,585,089). Nevertheless, even with FR amino acid back-substitution, certain antibodies cannot be humanized with retention of biological activity (Pichla et al., 1997). Therefore, there is no certainty that the murine HIRMAb 83-14 can be humanized even once the key murine CDR and FR amino acid sequences are known.